use Carp ();
$SIG{__WARN__} = \&Carp::cluck;

eval {
    use warnings;
    undef =~ m#1#;
}
[download]

which gives the following output:

Use of uninitialized value in pattern match (m//) at foo line 8.
        eval {...} called at foo line 6

Hope this helps.

Liz

I was testing that out and I realized something. It only gives you the exact line number of the error if you are using eval BLOCK, it gives much different (but still very useful) warnings if you are using eval EXPR

use Carp ();
$SIG{__WARN__} = \&Carp::cluck;
eval {
    use warnings;
    undef =~ m#1#;
};
$string = q{
    use warnings;
    undef =~ m#1#;
};
eval $string;

__OUTPUT__
Use of uninitialized value in pattern match (m//) at temp.pl line 5.
        eval {...} called at temp.pl line 3
Use of uninitialized value in pattern match (m//) at (eval 1) line 3.
        eval '
    use warnings;
    undef =~ m#1#;

;' called at temp.pl line 11
[download]

That is a very handy thing to remember.

--

flounder

There is a nice way to work out where the errors and warnings in eval code are coming from.

If you take a look in perlsyn#Plain-old-comments-(Not!), you'll see a feature that allows you to reset Perls idea of the current file and current line.

If you can use this to embed such a comment into each piece of evalable code, you can have perl tell you both the piece of code and the line number within it that at which the warning or error was encountered.

A crude demo...

P:\test>type test.pl8
#! perl -slw
use strict;

my $code = q[
#line 4000 "evalcode.pl"
print "hello";
print undef;
];

eval $code;

P:\test>test
hello
Use of uninitialized value in print at evalcode.pl line 4001.
[download]

By carefully choosing the names you give to your eval blocks (perhaps including the source file name/line number) you should be able to easily translate between the resultant error message and your code.

It would be really nice if it was possible to retroactively add this to eval'd code in CORE and CPAN modules. It sure would save a lot of searching when the messages arise from outside of your own code. Perhaps some sort of recommendation for a standardised filename/eval block/line number to module/source line mapping could be devised?

------
We are the carpenters and bricklayers of the Information Age.

The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

That is what i'm doing, unfortunately this site is about 20000 lines of perl, but i am beginning to isloate the problem.

I was hoping that there may be some way to get a more detailed warning, through some dash option - i'm pretty novice with eval.

Upgrade to 5.8.1, I recall this message is nicer to work with there.

I have tracked down the problem, my homecooked CGI descendent plays with param names, and in upgrading, i screwed up in a couple places.

Thanks much!